1. Field of the Invention
This invention relates generally to the dispersing of liquids into fluidized solids. More specifically this invention relates to an apparatus for dispersing a hydrocarbon feed into a stream of fluidized catalyst particles and for joining conduit sections.
2. Description of the Prior Art
There are a number of continuous cyclical processes employing fluidized solid techniques in which fluids are dispersed into a suspension of fluidized particles. One of the more important processes of this nature is the fluid catalytic cracking (FCC) process for the conversion of relatively high-boiling hydrocarbons to lighter hydrocarbons boiling in the heating oil or gasoline (or lighter) range. The hydrocarbon feed is contacted in one or more reaction zones with the particulate cracking catalyst maintained in a fluidized state under conditions suitable for the conversion of hydrocarbons. Carbonaceous materials are deposited on the solids in the reaction zone and the solids are conveyed during the course of the cycle to another zone where carbon deposits are at least partially removed by combustion in an oxygen-containing medium. The solids from the latter zone are subsequently withdrawn and reintroduced in whole or in part to the reaction zone.
It has been found that the method of contacting the feedstock with the catalyst can dramatically affect the performance of the reaction zone. Modern FCC units use a pipe reactor in the form of a large, usually vertical, riser in which a gaseous medium upwardly transports the catalyst in a fluidized state. Ideally the feed as it enters the riser is instantaneously dispersed throughout a stream of catalyst that is moving up the riser. A complete and instantaneous dispersal of feed across the entire cross section of the riser is not possible, but good results have been obtained by injecting a highly atomized feed into a pre-accelerated stream of catalyst particles. Pre-acceleration is often accomplished in a riser conduit with the use of a lift gas to lift the catalyst particles before they contact the feed. After the catalyst is moving up the riser it is contacted with the feed by injecting the feed into a downstream section of the riser. A good example of the use of lift gas in an FCC riser can be found in U.S. Pat. No. 4,479,870.
Most often fluid is injected into the fluidized particles from multiple points with separate injectors. U.S. Pat. No. 4,717,467 shows one method for injecting an FCC feed into an FCC riser from a plurality of discharge points in a non-radial manner. U.S. Pat. Nos. 5,554,341, 5,173,175, 4,832,825, and 3,654,140 all show the use of radially directed feed injection nozzles to introduce feed into an FCC riser. The nozzles are arranged in a circumferential band about the riser and inject feed toward the center of the riser. The angled feed nozzles are typical of those used to inject feed or other fluids at an intermediate portion in the riser conduit.
The angled feed injectors present a number of problems for the operation of the risers. The nozzles typically extend away from the wall of the riser and into the flow path of the catalyst. Passing particles over the nozzles at high velocity can result in erosion. An obvious solution to the problem of nozzle protrusion would be to recess the nozzles completely into the wall of the riser and thereby remove them from the catalyst flow path. This solution is not satisfactory since the feed injector tips are specifically designed to provide a relatively uniform coverage of the hydrocarbon feed over the cross-section of the riser by expanding the pattern of feed injection as it exits from the nozzle. Completely recessing the tips of the injector nozzles within the wall of the riser disrupts the ability to obtain a spray pattern over the majority of the riser cross-sectional area.
In addition, a long recognized objective when injecting liquids into fluidized particles is the maximization of the hydrocarbon feed dispersal into the particulate suspension. Dividing the liquid into small droplets improves dispersion of the feed by increasing the interaction between the liquid and solids. Preferably, the droplet sizes become small enough to permit vaporization of the liquid before it contacts the solids. It is well known that agitation or shearing can atomize a liquid hydrocarbon feed into fine droplets which are then directed at the fluidized solid particles.
A variety of methods are known for shearing such liquid streams into fine droplets. U.S. Pat. No. 3,071,540 discloses a feed injection apparatus for an FCC unit wherein a high velocity stream of steam, converges around a stream of oil upstream of an orifice through which the mixture of steam and oil is discharged. U.S. Pat. No. 4,434,049 shows another device for injecting a fine dispersion of oil droplets into a fluidized catalyst stream wherein the oil is first discharged through an orifice onto an impact surface located within a mixing tube. The mixing tube delivers a cross flow of steam which simultaneously contacts the liquid. In both cases the combined flow of oil and steam exits the conduit through an orifice which atomizes the feed into a dispersion of fine droplets and directs the dispersion into a stream of flowing catalyst particles.
For the most part, the injectors rely on relatively high fluid velocities and pressure drops to achieve atomization of the oil into fine droplets. The use of discharge orifices, spray nozzles and other distribution and atomization equipment is common in such injectors. Providing this high pressure drop and fluid velocity creates a harsh environment that can quickly erode the components of a feed injector. Therefore, it is routinely necessary to replace or refurbish portions of the injector that are exposed to this harsh environment, particularly the tip of the injector that is often exposed to high velocity particulate material. In addition the position or type of nozzle on or within the injector can greatly influence the type of dispersion obtained and can vary with the feed composition or flow rate. Therefore, it would be advantageous to quickly change out the components in a feed injector that need adjustment for particular feeds or replacing due to damage.
In addition, the need to replace damaged components may be reduced by the use of more refractory materials. For example, ceramic materials could greatly improve the durability of many feed distributor components. However, the inability to incorporate such materials into the usual stainless or carbon steel pipe components of the injector by welding or by the use of standard connections makes their use extremely difficult and has eliminated the presence of such materials from large commercial designs.
The usual placement of injectors further complicates the fashioning of suitable connections for easy replacement of components and for joining materials with diverse properties. Positioning feed injectors around a riser requires a minimization of the opening for the feed injector and results in a confined space that leaves little room for the injector components. This limited space provides little extra clearance for supplying connections.
A known type of piping connection uses a series of machined grooves on the ends of pipes that are connected by bridging links that have complementary grooves for engaging the grooves on the pipe ends. A sleeve or other retaining means is used to hold the link members against the pipes and the cooperating grooves in engagement. Different forms of these types of connections can be seen in U.S. Pat. Nos. 5,152,556, 5,265,917, 5,131,632, 3,687,487, and 4,159,132 3,687,487 mentions that it may be used with ceramic materials.
It is an object of this invention to provide an apparatus that incorporates diverse materials of construction into a feed injection nozzle.
It is a further object of this invention to provide a method and apparatus that simplifies the replacement of feed injector components.
It has now been discovered that low profile pipe connections can significantly improve the operation of a feed injector by making possible the use of different materials that were not readily joined in the past and facilitating the replacement of critical feed injector components. The incorporation of the connectors gives the injector additional versatility and maintainability through the use of internal connections of a low profile type. The injector apparatus has at least one connection that is positioned inside a retaining sleeve and connects the discharge tip of the injector to the piping that extends outside the sleeve and delivers the feed to the injector. This connection can join a ceramic nozzle tip to the rest of the injector assembly. The connection permits the ductile properties of the carbon steel or stainless steel feed piping to extend from the external piping into a contacting vessel before providing an abrasion resistant but brittle material that will extend the life of the nozzle tip. The injector tip can be made from an abrasion resistant material such as a ceramic, a solid stellite, or hastealloy.
As a result, the mechanical connections within the feed injector may be used to interchange the feed distribution nozzle as well as internal components of the feed injector. Changing the length of the internal pipe nozzle can reposition the shearing surface with respect to the nozzle opening that produces atomization of the feed. Different nozzles can adjustably regulate the area at the exit point of the nozzle to maintain the desired shear action on the feed with different feed flow rates.
The injector will also routinely incorporate an internal sleeve for separating two different fluids that enter the injector independently and undergo mixing therein. An additional internal connection may be added to the internal tube to facilitate the use of specific structures that promote mixing at the end of the tube. A connection near the end of the tube may be particularly useful for placing specially designed spray nozzles and other cast or machined devices at the end of the tube. In certain cases the outside of the connector can serve a dual purpose as a connector and as a flow restrictor to provide a pressure drop at the end of the tube.
A variety of low profile connections have been referenced with the prior art and can provide suitable connections. A low profile connection usually provides a mechanical connection having an outer radius that is typically no greater than the inner diameter of the pipe sections that it connects. For example a flange connection for a nominal 3-inch diameter pipe has an approximate outside diameter of 8 inches, whereas a typical low profile connection for the same nominal diameter has an outer diameter of only 5 inches.
The connection serves two basic functions. It joins the two pipe components structurally for transmitting loads or providing support while it also provides sealing. The connection for this application can be kept relatively simple in most cases since the support of the nozzle tip and tube will not normally impose high structural loads. In addition, since connections join pipe sections with open ends, the required sealing pressure of the connection should remain relatively low. Where operating temperatures permit their use, the low profile connection may incorporate an O-ring or other resilient sealing material in the contact faces of the connectors.
Low profile connections that are most suitable for use in this invention will be joined by relatively rectangular ribs and grooves. The term xe2x80x9crelatively rectangularxe2x80x9d refers to the profile of the groove and mating rib cross-sections which will have essentially flat bottoms and top with sides that have only a slight angle. The side angle of the grooves and ribs are preferably minimized to provide no more than the slope needed for sealing pressure and to facilitate disassembly. Excessive slope angle can create unnecessary sealing pressure resulting in local areas of high shear and tensile stress at the bottom of the rib or groove. Such local areas of high tensile and shear stresses can lead to the failure of many cast and ceramic materials that are otherwise desirable for their abrasion properties. Preferably, the sidewalls will make an angle with respect to a transverse plane of the connection of no more than 10xc2x0 and more preferably an angle of no more than 5xc2x0.
Feed injectors for use in this invention can be positioned in any vessel that contains particulate material for dispersion of the feed therein. The most common location anticipated for use of the feed injectors is in an FCC riser. Although the injectors may be used at any location in the riser, they will typically ring a transverse band somewhere in a middle section of the riser. The overall width of the band for retaining the injectors is preferably kept narrow.
Accordingly, in one embodiment, this invention is an injector apparatus for contacting catalyst with an at least partially liquid phase fluid in a contacting vessel. The apparatus includes a retaining sleeve fixed in the wall of the contacting vessel and an outer conduit adapted for insertion into the retaining sleeve and comprising a discharge portion and an inlet portion. The discharge portion defines a restricted opening by a discharge tip fixed at its distal end. An outside sleeve connection mechanically fixes the inlet portion to the retaining sleeve. The outside sleeve connection has a first part fixed about or near the outer end of the retaining sleeve. The first part is adapted to receive a second part of the outside sleeve connection that retains the inlet portion and is located outside of the vessel. An outer conduit connection mechanically joining the discharge portion to the inlet portion within the retaining sleeve. The outer connection includes a first half fixed to a proximate end of the discharge portion and defining a first plurality of transversely extended grooves on its outside surface and a second half fixed to a distal end of the inlet portion and defining a plurality of transversely extended grooves on its outside surface. A plurality of links hold the connection ends in sealed alignment by engagement of grooves on each end of the connection with ribs on each link. A locking member retains engagement of grooves until the connection is broken by removal of the locking member and the links.
In a more limited embodiment, this invention is an apparatus as previously described in the previous embodiment that also includes a tube having a discharge section and an inlet section. The inlet section has a proximate end fixed to the inlet portion and a distal end joined mechanically to a proximate end of the discharge section by a tube connection that is similar in construction and function to the outer connection. The tube and the inside of outer conduit define an annular flow path and the outside of the tube connection and inside of the outer conduit define a restricted passage along the annular flow path.
Additional objects, embodiments and details of this invention can be obtained from the following detailed description.